[Stoves] Lower PM in TLUDs than in stoves with fans

Thu Aug 29 22:54:58 CDT 2013

Dear Paul

Several agreeable things in that message:

>It is time to get serious about how TLUD stoves have superior performance.

Well, let's be cautious here, though I agree they are better than a lot of
things that came before. It just raises the bar. We can build very clean
stoves they are not TLUDs y'know.

>We can wait for Dean and Jim and ALL OTHER STOVE TESTING CENTERS to provide
some data.   

I look forward to people providing the spreadsheets, filled in, so those of
us who, like Jim, are adding metrics can do so based on the raw rata we
need.

1.  "Fan stoves" is a BAD name.   Any stove with a fan can be a "fan stove".

Exactly. No 'type' of stove is automatically 'good'. There are some terrible
TLUD's that I have tested (manufactured ones, not one-offs) and that
convinced me there are many things to get wrong with a TLUD. 

>What Jim and Dean are discussing are stoves that include Oorja, Biolite
(two models?), Philips, Reed Woodgas Campstove, maybe some units from China.
At least THREE different combustion regimes are included in the above named
stoves.   

There are dozens of different fan-assisted stoves in China. Some are TLUD's
and some are not.

2.  "Stoves with fans" is also not sufficiently specific, but at least they
could be recognized for what they are, which is, stoves of different types
that have fans.   

Agreed.

>.jets of air consume small quantities of pellet fuels in a small cup-type
combustion chamber.   For sure these are NOT TLUD stoves.  

Agreed. Having a fan is not a guarantee of anything other than it has a fan.

C.  They could be "Simple Improved Cookstoves - ICS - with fans".
Something like a bucket-stove with a fan blowing onto the flaming fuel.   No
examples come to mind, but add a fan and have a "fan stove."   

Agreed. Good point.

D.  They could be "TLUD stoves with fans".   Yes, TLUD stoves can be
operated with fans.   The opening statement is referring to natural draft
TLUD-ND having less  PM than TLUD-FA.     

That is not a helpful comment. Any stove type can be made better that it was
in the past. It is pointless to claim that a type of stove is cleaner
yatta-yatta. There are bad and good versions of every type of stove.

3.  So, one study that needs to be done is to compare the PM from TLUD-ND
and TLUD-FA.   Do such results already exist?    

I want to be clear that even if it did exist, it is an assessment of those
models at that time. No sweeping generalisations please. It is also
dependent on the protocol used. As Jim pointed out several times today in
the webinar, if the calculation of efficiency is made incorrectly, the stove
is incorrectly rated for efficiency. As the same calculation that provides
the energy number for the efficiency is converted to 'dry fuel equivalent'
(meaning equivalent to that amount of energy) and that is in turn
'understood' to be the fuel consumption, there are serious implications if
the protocol used does not correctly assess what to do with the charcoal.
'Misleading claims' is perhaps a better expression.

4.  BUT.   Yes, there is a BIG BUT to be considered.   This is because
TLUD-FA (those with fans) have been blatantly mis-used and the test results
could be erroneous because the test was not stopped when the TLUD pyrolysis
process stopped, which is when the bottom burning of char started and
continued as long as operators were feeding in raw fuel at the top.  

There are all sorts of issues affecting the test results for these stoves.
It is a major point of discussion as to whether the test is supposed to
assess the fuel consumption in real life (meaning as used) or assess the
heat transfer efficiency because some designer wants to know what it is. The
protocols and calculations are quite different. If the stove cannot normally
be extinguished, then why would the fuel remaining at the end of cooking be
credited as 'not having been burned' when there is no way to turn it off and
even it if did, the fuel cannot be used in the next fire (in some cases).
The fuel consumed from the supply each time the task is replicated is the
fuel consumption. No getting around it by fancy mathematics. We have to keep
our eye on that figure because in almost all cases stove programme are
intending to reduce that consumption per household per day.

I repeat:  the TLUD testing needs to be stopped when the TLUD pyrolysis
process stopped, which is when the bottom burning of char started and
continued as long as operators were feeding in raw fuel at the top.  

I think you are going to have to sell the idea that a) it can be stopped and
b) that if it does, less fuel will be used.

Are you thinking of fuel consumption or CO and PM as the issue? What is
prevented/avoided if the test is stopped at some well-described time?

In conclusion, let's get our understanding clear that the addition of a fan
to a stove does NOT automatically put that stove into the Tier 3 and Tier 4
categories of low PM emissions.   FIRST think of what kind of combustion the
stove utilizes:   simple ICS, Rocket, TLUD, other micro-gasification, other
....    THEN consider if it has a fan in it.  

Agreed.

STATEMENT:  I believe that the TLUD stoves (whether ND or FA) are cleaner
about PM than the other combustion regimes because the process of pyrolysis
leaves the inert materials (non-combustibles known as ash) held tightly to
the charcoal that is created.   So, do NOT burn the charcoal.   Especially
do not burn it with vigorous streams of air at the level of the charcoal.
[And there are probably additional variables to be studied.]

This hypothesis remains to be proven.   

I don't think this will stand up to scrutiny because there are lots of ways
to burn fuel. The point about the ash being lofted is a major one. If fans
blow the ash into the air and it gets away, there is OM but is it dangerous
PM? Is a condensed volatile compound a lot more dangerous? Perhaps the BC vs
OC split is more important than the mass of PM2.5.

Quick note to Dean in reply about the mass of PM - the mass of the
nanoparticles is so small that it is difficult to estimate what the
influence is, if there is a large filter picking up everything up to PM10.
My point is that there seems to be a bit of chatter about counting the
number of particles when they are small, but determining the mass. This it
is not much help to collect the UFP on the same filter as there is hardly
anything there. I hoped it would be easier but it is not.

But while we wait for the test results, money will be channeled to other
stove technologies, field tests of health will be conducted withOUT having a
TLUD stove included in the study, and people will continue to suffer (and
some will die) because of the high PM levels in household cookstoves.  It is
late 2013 and studies of TLUD stoves are only scratching the surface of what
things need to be studied.

I hear you. I do not hear you exclusively, however. There are other ways to
burn very cleanly with extremely low PM. If you want to get a hearing you
will have to (as far as I see it) include any stove that burns really well,
not just TLUDs, however much they are loved in some circles. Everything that
is clean and good about a TLUD applies to crossdraft stoves, plus they can
be refuelled and if you like, char can be harvested periodically.

You are asking for the ear of generalists (testers) while proposing
specialist interests. Assessing a stove is going to cost about a grand.
Bring money, I guess.

Tell you want, how about providing a list of exactly the tests you think
should be performed that would give the most bang for the buck. What do you
feel needs to be shown? 

I believe it is the heat flux rate, the CO and PM per net MJ in the pot, and
the system efficiency, plus char mass remaining (but not analysed). Those
can all be assessed at the same time. That would give you fuel consumption,
specific emissions per MJ, and a power rating. If you have that for a dozen
stoves would you be happy?

I would propose that all the data be made available with the proviso that
the producer of the data owns it for publication purposes. They should
co-author anything that uses it.

How does that sound?

Thanks
Crispin

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